Today, people are increasingly aware of the importance of environmental protection. Energy saving is especially necessary to help the environment which, in turn, helps the quality of life. The focus on low carbon emission during daily traffic use is especially important for the health of the public in carbon areas. In view of this, a bicycle serves as a useful tool for reducing the carbon footprint while being used for activities including short-distance commuting, leisure journeys, physical exercise, and so forth.
In a prior-art technique, an alert device for alerting a speed change of a bicycle includes an accelerometer and a brake light. The alert device detects a predetermined deceleration condition of the bicycle by using the accelerometer to turn on the brake light.
U.S. Pat. No. 7,649,447 B2 discloses a wireless bike brake light. U.S. Pat. No. 8,717,155 B2 discloses a brake warning device and method. U.S. Patent Publication No. 2004/0032324 A1 discloses a brake light controller. In general, it is necessary for a brake warning device to perform a low-pass filtering operation in the disclosures in the prior art. Although the low-pass filtering operation can eliminate a relatively-high frequency vibration noise, it can also influence or filter out another acceleration signal that is necessary for lighting up an alerting device.